Melt butter in a medium-sized pan. Sauté onion in butter until onions are clear.
Add garlic and salmon. Sauté at medium to low heat for about 2 more minutes until the salmon is lightly cooked.
Add the cream, lemon juice, lemon pepper and black pepper. Stir constantly until thickened. Sauce should be very thick once you have added all the cream.
Add tomato and stir carefully until tomatoes have softened.